Scale-Up CFD Analysis of Spray Towers for CO2 Absorption: Design Implications of Multi-Stage Spray Architectures

Spray absorption offers a promising route for post-combustion CO 2 capture within carbon capture and storage systems, but scaling to industrial towers requires effective control of droplet spatial distribution and fresh-solvent availability, rather than increasing tower size or solvent flow rate alone. This work extends a previously validated Eulerian–Lagrangian reactive computational fluid dynamics (CFD) framework for NaOH-based CO 2 absorption to a 15 m-high, 3 m-diameter tower with up to 39 injectors across three vertical levels. Parameters examined include gas inlet configuration, injector number, spray cone angle, vertical staging, level spacing, injection orientation, operating pressure, and spray atomization. Absorber performance is governed primarily by droplet distribution and fresh-solvent availability along the gas path. At fixed total liquid flow rate, increasing the number of injectors from one to six raised removal efficiency from 35–40% to 90–95%. Increasing the cone angle from 60 ∘ to 100 ∘ raised CO 2 removal efficiency from 74% to 85%, an absolute gain of 11 percentage points. Multi-level injection supplies fresh reactive droplets along the gas path and extends the active absorption region, while configurations that maintain solvent availability near the outlet better support residual CO 2 removal. Elevated pressure further increases the attainable capture level; for the finer spray case, increasing pressure from 1 to 5 bar raised removal efficiency from roughly 80% to nearly complete removal. Overall, the scale-up results indicate that high CO 2 removal requires uniform droplet distribution across the tower, continued fresh-solvent availability along the gas path, and coordinated use of finer atomization and elevated pressure to enhance gas–liquid mass transfer.